Answer:
The plan for banning slavery in territory gained from Mexico was called the Wilmot Proviso.
Step-by-step explanation:
The Wilmot Proviso was a submission filed on August 8, 1846 by David Wilmot, a member of the House of Representatives, in the US Congress. He said that slavery could not be introduced in the vast areas that had fallen to the United States during the Mexican-American War. The application was filed several times over the next few years, but it was never passed. This failed mainly because of the resistance in the Senate. It is considered one of the incidents leading to the Civil War.